The present invention refers to an automatic apparatus for feeding elongated work-pieces, such as bars and the like, to multi-spindle machine tools and, more generally refers to improvements to the drive devices of the bar pushing members in bar feeders of rotating drum type, for allowing a selective operation when the feeder drum is at a standstill with a guide for the bars in a predetermined angular position, as well as when the drum is rotationally actuated by the same machine tool. In this way it is possible to anticipate the forward movement of the bars while each spindle of the machine tool is rotating and approaching a predetermined working position.
Automatic apparatuses for loading and feeding bars to be worked to multi-spindle machine tools are generally well known. Typically, such an apparatus comprises a frame member for supporting a bar guide drum that rotates about a horizontal axis coinciding with the rotational axis of the spindle-holder turret of the machine tool. Bar guides longitudinally extending with respect to the drum are provided in angular spaced apart positions and axially aligned to corresponding spindles of the machine tool, each guide for the bars being provided with a bar-pushing member selectively operated to move a bar forward through a respective spindle of the machine, when the drum is at a standstill, and the guide is in a predetermined angular position.
Apparatuses of the above mentioned type are shown and described in several prior patents, for example in U.S. Pat. No. 3,874,519, U.S. Pat. No. 3,955,687, U.S. Pat. No. 4,088,230, U.S. Pat. No. 4,122,735, U.S. Pat. No. 4,292,864, U.S. Pat. No. 4,604,924 and U.S. Pat. No. 4,700,593.
It is also well known that in multi-spindle automatic lathes the working speed is constantly increased and the operative cycles are correspondingly reduced to increase production rates. Consequently the structure and the operative mode of the bar feeder automatic apparatuses were improved to satisfy the new and increased requirements of these machine tools.
For example, a prior European Patent Application EP-A-O 123 658 discloses a drive device for the bar pushing members of a drum feeder of the known type, which uses a mechanical drive device comprising a plurality of gear members operationally connected by endless chains to a respective bar-pushing member. The various gears are radially arranged with their axes at one end of the drum to rotate with the latter, and gear coupling means are provided to connect each gear member to a power operated conical gear co-axially arranged with respect to the drum. A circular cam acts on the coupling means to selectively connect each pushing member to a drive motor of the central conical gear while the drum of the feeder is rotating and a selected one of the bar guides is approaching to a predetermined angular position.
This solution, even if allowing the forward movement of the bars as soon as the spindle collets of the machine tool are opened while the feeder drum is rotating, in practice presents quite a complex structure which, because of the delays caused by the coupling backlashes, does not allow for perfect synchronization during operation of the device. Moreover, the more complex coupling system at one end of the drum, with its own weight and inertia negatively affects the drum by opposing to the rotational force exerted by the machine tool itself. The use of such a drive device does not allow operation at high rotational speeds, and therefore the feeder cannot be used in machine tools of the fast type. Moreover, the extreme mechanical complexity of the drive device makes it difficult to set-up, and causes higher breakdown risks due to bad coupling operation and higher maintenance costs.
In order to improve such a feeder, European Patent Application EP-A-0 174 034, discloses another mechanical solution, which is simplified in some particulars, but however employs teeth couplings connectable to the pushing members and operating only when the drum is at a standstill when each guide for the bars is in an angular position where the bars can be moved forward in the respective spindle of the machine tool.
Although with this second solution the bar feeder is simplified and the entire weight of the drum is partially reduced, it does not allow for an anticipated feeding of the bars when the drum is revolving. Therefore it cannot be used in machine tools of the fast type.
In a further European Patent Application, EP-A-0 338 606, an hydraulic solution has been suggested, according to which hydraulic drive motors are used for each pushing member, wherein the various hydraulic motors are supported at one end of the drum to be selectively fed by a suitable rotating oil distributor.
This document suggests only a different solution to the problem of the anticipated forward movement of the bars, without achieving the aim of simplifying the feeder construction and substantially reducing the weight of the rotating bar guide drum.
On the contrary, under some points of view, this hydraulic solution is quite worse with respect to a mechanical solution, as the higher weight of the hydraulic motors and of the oil herein contained, constitute a concentrated mass which can cause distortions to the drum when the latter is under rapid rotation, thus requiring drums having a sturdy construction and consequently a higher weight.